In a pressurized bed combustion power plant, a so called PFBC-power plant, the hot combustioned gases are guided from the fluidized bed combuster through cyclones, for purification, in a hot gas channel, to a gas turbine. The shaft of the gas turbine drives a compressor, compressing the combustion air which, through an air supply channel, is supplied to the fluidized bed combuster. The hot gas channel is arranged concentrically in the air supply channel and, accordingly, the hot gas channel is surrounded by the air which is supplied to the combuster. To be able to shut off the flow of hot gas to the gas turbine, for instance in case of a gas turbine trip, a throttle valve is arranged in the proximity of the hot gas channel inlet to the gas turbine. This throttle valve is arranged on a shaft which is turnably supported by means of bearings arranged in the wall of the hot gas channel. Due to the high temperature, approximately 850.degree.-870.degree. C., existing in the hot gas channel, damages often occur on the shaft bearings, as heat is led through the shaft of the throttle valve into the bearings. This can lead to that the throttle valve does not work when the gas turbine has to a problem be quickly stopped.